Mechanical seals are used on the rotatable shafts of rotating equipment to prevent or minimize leakage of a process fluid being handled by the rotating equipment. For example, pumps are used to pump process fluids through a pump casing by impellers. The rotatable shaft is typically supported by bearing assemblies and projects into the pump casing to drive the impeller. The mechanical seal is provided on the shaft to seal the process fluid chamber from the pump exterior, and in particular, prevent or minimize leakage of the process fluid along the shaft to the pump exterior. For many small scale applications, or applications where the impeller does not encounter excessive wear, the mechanical seal and shaft may be located in fixed locations. Should the impeller wear after a significant life cycle, the impeller may simply be replaced.
In some applications, the process fluid may generate substantial wear on the impeller, for example, if the process fluid includes a high volume or high concentration of abrasive solids that are combined with a liquid to form a slurry. These slurries pass through the impeller and can lead to significant wear of the impeller surfaces. When encountering a high wear rate of the impeller, it is undesirable to frequently replace an impeller since frequent replacement increases the operational costs of the pump and associated seal. In these circumstances, it is known in smaller scale applications to permit adjustment of the axial position of the shaft to shift the impeller axially within the pump chamber to increase the performance of the impeller as it wears and thereby extend the life cycle of such impeller. For these circumstances, mechanical seals have been designed which have a stationary housing and a gland that supports the seal rings wherein the gland is movable axially within the stationary housing so that the seal rings can move together with the shaft while still performing the sealing function. An example of one such seal is disclosed in U.S. Pat. No. 4,575,306 (Monnot) which is a component seal requiring assembly of the individual components during installation. Other examples include U.S. Pat. No. 3,977,737 (Grzina) and U.S. Pat. No. 4,509,773 (Wentworth).
While slurries have been handled in small scale applications, significant challenges are created in large scale hydro transport applications which require large high-pressure slurry pumps to pump slurries substantial distances. In particular, large high pressure slurry pumps used in applications such as hydro transport applications including tailings applications in the Mineral and Ore Processing (M&OP) industry wherein these pumps require either single or double pressurized slurry seals. These applications also include large moderately abrasive low pressure pumps found in Flue Gas Desulfurization (FGD) pumps.
These applications can be extremely abrasive requiring frequent impeller adjustment and replacement of high-wear, wet-end pump parts and mechanical seal components. These types of pumps exhibit ample register fits of cast components as well as internal clearances of bearings, and significant pump casing deflections from the high pressure and pipe strain encountered in use, which typically results in large shaft movement and seal face flange alignments.
Examples of such high pressure slurry pumps include Model HTP 500 and 600 pumps commercially sold by Weir which are used in oil sands hydro transport and tailings applications. These pumps include a shaft sleeve on the rotatable shaft, and a stuffing box disposed in surrounding relation to the shaft whereby a stuffing box chamber is formed that is filled with a plurality of axially adjacent packing rings. However, these packing rings typically permit leakage along the shaft and therefore, can incur significant water leakage costs and pump maintenance costs. This is particularly undesirable in remote facilities where a ready supply of water is not available or is not cost effective.
It therefore is an object of the invention to provide a mechanical seal that is suitable for installation in large slurry pumps which are being used in applications such as tailings transfer and tar sands ore transport.
The pumps for these large scale applications, such as the Weir HTP 500 and 600 pumps, are developed for pump speeds up to 500 RPM, and high pressure conditions which may reach 4000 kPa (580 psi) which can be the maximum allowable working pressure of the pump during operation, and reach 6000 kPa (870 psi) pressure which may occur during static hydro testing of the pump. Hydro transport and tailings slurries can be expected to have over 50 percent solids by weight. In some applications, maximum particle size can be 5″×5″×12″ coming through worn 5″×5″ screens, which may therefore require a full coverage back liner to protect the seal when mounted to the shaft. The seal in the inventive design preferably will accommodate 62 mm (2.5 inch) axial adjustment to allow for impeller adjustment which is needed in such applications due to the aggressive wear expected on the suction side liner, wherein the worst case for shaft run out may be over 0.030 in. radial, and over 0.076 in. TIR (total indicated reading) due to bearing clearances, shaft run out, and sleeve to shaft clearance and concentricity. Radial deflection typically will be at the bottom with a new impeller, and impeller wear will cause imbalance creating an orbit about the radial clearances. Further, the seal will need to accommodate a fraction of an inch TIR measured out of perpendicularity of the seal mounting surface and a quarter inch TIR concentricity with respect to the shaft due to standard slurry pump manufacturing tolerances and expected wear to the interface between a bearing assembly and bearing assembly mounting surface on a pump bearing assembly base which mounts next to the pump casing and rotatably supports the shaft. The improved seal preferably will need to accommodate impeller replacement every 2000 to 3000 hours and impeller adjustments by axial adjustment of the shaft approximately every 1000 hours or even less. Further, the mechanical seal preferably includes a barrier fluid at a desired pressure, wherein the seal is designed to handle a full process pressure of 580 psi in the event of a loss of barrier pressure.
The mechanical seal of the invention relates to a cartridge seal developed for such pumps which eliminates problems with the fitment and performance of conventional cartridge seal designs if used on large slurry pumps that have an axially adjustable shaft, wherein the inventive mechanical seal is installed from the pump wet end and maintains all advantages of a cartridge seal. The basic concept involves rigidly mounting stationary or non-rotatable gland components to the bearing housing and mounting the seal rings and associated gland components to the shaft wherein the seal rings and associated gland components are movable axially with both the shaft and the associated bearing assembly during impeller adjustment. A secondary seal is formed between the stationary and movable gland components to allow for this axial shaft adjustment.
The seal rings and associated seal faces are integrated into a single shaft sleeve wherein the single shaft sleeve eliminates a sleeve on sleeve arrangement that typically is used in the currently available slurry seals. Providing this seal face and shaft sleeve arrangement also reduces the seal face diameter. The seal sleeve of the invention preferably has the same ID, end dimensions, and face seals as the OEM shaft sleeve it will replace. This eliminates a seal locking collar which serves to eliminate problematic seal sleeve to pump sleeve galling that often occurs during installation, removal, and during periodic impeller adjustments of the known slurry pumps, as well as galling that results from slurry jamming into close diametrical fits between the sleeves. Eliminating a locking collar avoids resultant limitations on test pressure, and also reduces overall length.
In the inventive cartridge seal, a stationary housing or seal adapter mounts to the pump casing and includes an adapter ring that sealingly contacts the movable gland wherein setting plates preferably locate the gland to the shaft sleeve both concentrically and axially within the axial tolerance of the shaft relative to the bearing housing. The seal adapter or stationary housing and cooperating gland are cylindrical which eliminates a conventional cartridge flange and allows for a reduction in the size of these components so as to fit through the pump's wet end back liner. The adapter ring preferably pilots on or aligns with the gland and is not piloted to the pump interface which allows the adapter ring and associated seal adapter to mount to the pump casing when piloted to the gland which thereby accommodates large concentric pump misalignments that is common on these pumps. For example, these misalignments may be about 0.25 inches in TIR on the HTP 600 pump.
A static or stationary gland gasket is disposed on the seal adapter and is captured by an associated end plate that mounts to the adapter ring so that the gasket sealingly contacts the movable gland. The static gasket provides a static seal between the movable seal gland and the seal adapter by tightening bolts on the end plate to thereby compress the gasket between the end plate and adapter ring and squeeze the gasket into improved sealing contact with the movable gland. Axial movement of the shaft during impeller adjustment is accommodated via the static gasket which contacts the OD of the movable gland, which is axially-shiftable, wherein the static gasket preferably projects radially inwardly from the opposing ID surface of the seal adapter and the adapter ring thereof and thereby projects toward the OD of the movable gland. This axial shaft adjustment can be made easier by reducing compression of the static gland gasket through loosening or removing the end plate and static gasket if desired, although gasket decompression or removal may not be required.
Conventional cartridge mechanical seals do not satisfy the requirements of large high pressure slurry pumps practically, reliably, or realistically. However, the improved mechanical seal accommodates the challenging conditions typically encountered on these large, high pressure slurry pumps and provides other advantages relating to installation, removal, preventive maintenance, field replacement of the primary seal, and operation as described in further detail below.
More particularly, the improved mechanical seal of the invention preferably provides various advantages over prior mechanical seals. The advantages include:
1. Seal cartridge weight is minimized by eliminating a large diameter gland flange which are used in smaller scale cartridge seals, which is a particular advantage since the gland will have approximately a 27 in. diameter on the known HTP pumps.
2. Eliminating the existing seal sleeve in the known pumps minimizes seal face insert size.
3. Galling of the seal sleeve to pump sleeve and/or setting plates due to required shaft rotation during impeller installation, removal, and clearance adjustments is eliminated in the improved mechanical seal. The improved seal is designed to permit periodic impeller adjustments to accommodate impeller life of 2000 to 3000 hours with periodic impeller axial adjustments up to 2.5 in. every 1000 hours of operation.
4. Improved run-out of rotating seal parts by eliminating clearance and tolerance between sleeves.
5. Seal removal is facilitated by eliminating migration of packed slurry between conventional seal sleeve and pump sleeve on the process fluid side as well as atmospheric side due to both normal and failure leakage. The inventive seal sleeve is sealed on the axial facing ends which thereby isolates the shaft fit from slurry and allows liberal grease to be used between the shaft and shaft sleeve for ease of installation and removal of the inventive seal.
6. The inventive seal design requires less customer/user knowledge and skill to install the mechanical seal on the shaft when compared to conventional mechanical seals on slurry pumps. Subsequent impeller adjustments do not affect seal setting or seal face wear track alignment.
7. A seal sleeve locking or clamp collar engaging the pump shaft is eliminated which is problematic in slurry applications due to dirt, grease, and galling between the sleeves wherein the locking collar can slip during operation or else gall during seal installation because lubrication is not permitted with a clamp collar. Where a locking collar is used, repositioning is required for subsequent impeller adjustments. Also, hydrostatic test pressures are typically limited by the locking collar clamping force, but such limitations are avoided in the inventive cartridge seal.
8. Wet end design wherein the inventive seal is installed on the shaft from the wet end which thereby serves to ease installation and removal.
9. The inventive seal uses a non piloted centering, seal adapter which is located by the seal gland outside diameter and is centrically located to the seal/pump sleeve via setting plates on each end of the seal to thereby accommodate large non-concentric seal adapter alignment.
10. The seal adapter static gasket in the inventive design preferably is an O-ring and is compressed and sealed to the seal gland outside diameter after impeller installation and adjustment is complete, wherein the gasket is a packed gasket and uses an O-Ring end plate and bolts to effect compression. The gasket compression can be released during subsequent impeller adjustments and the annular gasket could be replaced with a new one that is separated at one location for installation and then glued together at the free ends to reform the continuous annular ring shape.
11. Periodic impeller adjustments do not affect the seal setting.
12. Affords maximum utilization of axial space in the pump seal cavity for double seal outboard seal selection and impeller adjustments.
13. Primary seal faces are shrouded from impact by large slurry particles by a tapered gland extension that moves with the seal ring and movable gland and thereby maintains an axial position relative to the seal rings throughout the 2.5 in. axial impeller adjustment range.
14. Seal cavity geometry is maintained between the impeller hub, seal rotating assembly, which comprises the seal rings and movable gland, and the tapered gland extension that is exposed to process slurry, wherein the seal cavity geometry is maintained throughout the 2.5 in. axial shaft position. This geometry controls and impedes erosion of metal parts and serves to shroud the inboard seal faces from the impact of large slurry particles. With conventional cartridge designs, the seal remains stationary if the shaft is moved axially, such that 2.5 in. of axial shaft movement would increase the gap between the seal and impeller creating a high erosive vortex and exposing the seal faces and pump shaft to impact and erosion by larger slurry particles.
15. The improved seal design facilitates a complete replacement (repair) of the high wear primary seal components during impeller replacement without requiring removal of the complete seal from the pump or disturbing seal adjustment which thereby facilitates economic preventive maintenance. In this regard, orbital shaft movement of up to 0.1 in. TIR typical will cause high primary seal face wear at the outside diameter seal interface by wiping slurry into the seal face OD every revolution. Pump and system operating factor will be increased by eliminating catastrophic seal failures which typically cause pump system water hammer and other equipment damage from an emergency system shut down.
16. The stationary or non-rotatable seal components, including the movable gland, are mounted rigidly to the bearing housing so as to move therewith during axial shaft adjustment. Rigid mounting of the seal stationary components to the bearing housing thereby corrects axial setting of these components and eliminates installer discretion. The seal setting is not affected by pump casing movement caused by casing pressure expansion, or piping strain, which can be problematic in large slurry pumps. Axial, angular, and to some degree concentric movement is accommodated by the static gland gasket and does not affect alignment of the rotating seal components with the stationary gland components.
17. Plan 54 & 32 barrier piping is permanently mounted to a stationary clamp ring that is used to mount the movable gland and bearing housing together. The clamp ring has sealed ports which communicate with the gland for supplying fluid to the seal gins. Removal is not necessary for seal installation and replacement.
18. The seal design economically accommodates a single seal design utilizing the same adaptive hardware by simply changing the sleeve and components of the movable gland.
19. An installation tool is designed to facilitate field installation and removal which will include a weight centered lifting lug and include a bolted attachment to the pump shaft end.
Therefore, the inventive mechanical seal provides a cartridge seal design to large scale, high-wear pumps, and provides significant advantages as discussed herein.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “up”, “down”, “right” and left” will designate directions in the drawings to which reference is made. The words “in” and “out” will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. The words “proximal” and “distal” will refer to the orientation of an element with respect to the device. Such terminology will include derivatives and words of similar import.